Center section for a hydrostatic transaxle

ABSTRACT

A center section for a hydraulic pump and motor mounted in a transaxle casing. The center section has a protuberance formed thereon, a pair of flat surfaces separate from the protuberance and at least one fastener opening formed in the center section for receiving a fastener engaged to the casing. The protuberance is adapted to mate with a center section locator formed in the casing to establish an X-Y orientation for a central axis while the fastener provides a Z-axis locator for the center section.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a divisional application of and claimspriority from application Ser. No. 10/209,703, filed Jul. 31, 2002 nowU.S. Pat. No. 6,775,976. That application is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates generally to hydrostatic transaxles.

Hydrostatic transaxles (“HSTs”), including integrated hydrostatictransaxles (“IHTs”), are known in the art and are more fully describedin, among others, U.S. Pat. No. 5,314,387, which is incorporated hereinby reference in its entirety. Generally, an HST includes a centersection or the like on which is mounted a hydraulic pump and a hydraulicmotor. The hydraulic pump and the hydraulic motor each carry a pluralityof reciprocating pistons that are in fluid communication through portingformed in the center section. As the hydraulic pump rotates, the pumppistons move axially as they bear against an adjustable swash platewhere the degree of axial movement depends upon the angular orientationof the swash plate. Axial movement of the pump pistons forces ahydraulic fluid through the porting, which forces the motor pistonsagainst a thrust bearing to thereby rotate the hydraulic motor. As thehydraulic motor rotates, hydraulic fluid is returned to the hydraulicpump through the porting. In this manner, the rotation of the hydraulicpump is translated to the hydraulic motor and the rotation of thehydraulic motor may be used to drive one or more axles of a riding lawnmower, small tractor, or the like.

Zero-turn, hydrostatic transaxles (HZTs) are also known in the art.Generally, an HZT is utilized in connection with a vehicle to providefor the independent control of each of the drive wheels of the vehicle.By way of example, HZTs are described in U.S. Pat. Nos. 5,078,222 and6,283,235 which are incorporated herein by reference in their entirety.Additionally, Eaton has developed and marketed HZTs as their models 771and 781. The Eaton model 771 is an assembly with one pump and one motorwhere two Eaton model 771 assemblies, a right and a left, are requiredfor zero turn drive. The Eaton model 781 consists of two units similarto the Eaton model 771 but joined together to make one assembly.

SUMMARY OF THE INVENTION

A pair of zero-turn, hydrostatic transaxles (HZTs) that may be joined toform an integrated, zero-turn, hydrostatic transaxle. While the controlarm and brake mechanism associated with an HZT can be mounted on eitherthe inboard or outboard side of the HZT casing, in one embodiment, anintegrated, inboard brake mechanism is provided for the joined HZTs. Inyet another embodiment, the casing of each HZT is provided with bossesand a flat section that are arranged to extend outward from the casingto create an area of space between the joined HZTs. In a still furtherembodiment, left and right center sections that are substantial mirrorimages of each other are provided for each HZT wherein each centersection has unique features that allows the center section to becorrectly oriented within its HZT casing. In an illustrated embodiment,the center section of an HZT is disposed within the casing in a locationthat is below a horizontal plane that passes through a center axis ofthe HZT axle shaft. In another illustrated embodiment, the integratedHZTs comprises a first casing section, a second casing section, and athird casing section that is disposed intermediate the first and secondcasing sections.

A better understanding of the objects, advantages, features, propertiesand relationships of the invention will be obtained from the followingdetailed description and accompanying drawings which set forthillustrative embodiments that are indicative of the various ways inwhich the principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference may be had topreferred embodiments shown in the following drawings in which:

FIG. 1 illustrates a perspective view of an exemplary, integrated,zero-turn, hydrostatic transaxle constructed in accordance with theprinciples of the subject invention further illustrating an exemplary,outboard, disk brake mechanism and various casing attachment mechanisms;

FIG. 2 illustrates a perspective view of the integrated, zero-turnhydrostatic transaxle of FIG. 1 with an exemplary bracket attachmentmechanism;

FIG. 3 illustrates a perspective view of the integrated, zero-turnhydrostatic transaxle of FIG. 1 with an exemplary, inboard, disk brakemechanism;

FIG. 4 illustrates an exploded view of exemplary casing members andcenter sections of the integrated, zero-turn hydrostatic transaxle ofFIG. 1;

FIG. 5 illustrates an exploded view of the integrated, zero-turnhydrostatic transaxle of FIG. 3 particularly illustrating the exemplary,inboard, disk brake mechanism and attachment hardware;

FIG. 6 illustrates a perspective view of a further exemplary embodimentof the integrated, zero-turn hydrostatic transaxle of FIG. 1 wherein asingle plate replaces the cap members of the casings;

FIG. 7 illustrates a perspective view of yet another exemplaryembodiment of the integrated, zero-turn hydrostatic transaxle of FIG. 1wherein a single internal plate replaces the cap members of the casings;

FIG. 8 illustrates an exploded view of the integrated, zero-turnhydrostatic transaxle of FIG. 6;

FIG. 9 illustrates an exploded view of the integrated, zero-turnhydrostatic transaxle of FIG. 7;

FIG. 10 illustrates a perspective view of an exemplary, zero-turn,hydrostatic transaxle used to form the integrated zero-turn, hydrostatictransaxle of FIG. 1 further illustrating an exemplary, inboard, diskbrake mechanism and outboard control arm mechanism;

FIG. 11 illustrates a perspective view of the exemplary zero-turn,hydrostatic transaxle of FIG. 10 further illustrating an exemplary,inboard, cog brake mechanism and outboard control arm mechanism;

FIG. 12 illustrates a perspective view of the exemplary, zero-turn,hydrostatic transaxle of FIG. 10 further illustrating an exemplary,inboard, disk brake mechanism and inboard control arm mechanism;

FIG. 13 illustrates a top view of the exemplary, zero-turn, hydrostatictransaxle of FIG. 12;

FIG. 14 illustrates a perspective view of the exemplary, zero-turn,hydrostatic transaxle of FIG. 10 further illustrating an exemplary,outboard, disk brake mechanism and outboard control arm mechanism;

FIG. 15 illustrates a top view of the exemplary, zero-turn, hydrostatictransaxle of FIG. 14;

FIG. 16 illustrates a side view of the exemplary, zero-turn, hydrostatictransaxle of FIG. 12 with the cap member removed;

FIG. 17 illustrates an exploded view of the exemplary, zero-turn,hydrostatic transaxle of FIG. 12 particularly illustrating an exemplarycenter section, filter mechanism, and attachment hardware;

FIG. 18 illustrates a cross-sectional view of the exemplary, zero-turn,hydrostatic transaxle along line A—A of FIG. 15 with an exemplary,outboard control arm mechanism and outboard brake mechanism;

FIG. 19 illustrates a cross-sectional view of the exemplary, zero-turn,hydrostatic transaxle along line A—A of FIG. 15 with an exemplary,inboard control arm mechanism and inboard brake mechanism;

FIG. 20 illustrates a cross-sectional view of the exemplary, zero-turn,hydrostatic transaxle along line B—B of FIG. 15;

FIG. 21 illustrates a cross-sectional view of the exemplary, zero-turn,hydrostatic transaxle along line C—C of FIG. 13;

FIG. 22 illustrates a cross-sectional view of the exemplary, zero-turn,hydrostatic transaxle along line D—D of FIG. 13;

FIG. 23 illustrates an exploded view of an exemplary bypass mechanismand internal expansion tank cover for use in connection with theintegrated, zero-turn, hydrostatic transaxle of FIG. 1;

FIG. 24 illustrates a pump end view of exemplary center sections for usein connection with the integrated, zero-turn, hydrostatic transaxle ofFIG. 1;

FIG. 25 illustrates a motor end view of the exemplary center sections ofFIG. 24;

FIG. 26 illustrates a top view of the exemplary center sections of FIG.24;

FIG. 27 illustrates a cross-sectional view of the exemplary centersections along lines E—E of FIG. 26;

FIG. 28 illustrates an exploded view of an exemplary filter assembly foruse in connection with the integrated, zero-turn hydrostatic transaxleof FIG. 1;

DETAILED DESCRIPTION

Turning now to the figures, wherein like reference numerals refer tolike elements, there is illustrated a zero-turn, hydrostatic transaxlegenerally used to drive a vehicle, such as a walk behind mover, snowthrower, riding mower, tractor, or other vehicle desiring a zero turnradius. As particularly illustrated in FIGS. 1–9, the zero-turn,hydrostatic transaxle is comprised of a pair of generally mirror imageHZTs 10L and 10R that are each used to independently drive a single axleshaft 24. While the HZTs 10L and 10R can be used independently, the HZTs10L and 10R may be adapted to be attached to one another in a mannerdescribed hereinafter to form an integrated, zero-turn, hydrostatictransaxle.

As will be understood by those of skill in the art, and as particularlyillustrated in FIGS. 16–22, each HZT 10 generally operates on theprinciple of an input shaft 12 rotatably driving a hydraulic pump 14which, through the action of its pump pistons 16, pushes hydraulic fluidto a hydraulic motor 18 through porting formed in a center section 20 tocause the rotation of the hydraulic motor 18. The rotation of thehydraulic motor 18 causes the rotation of a motor shaft 22 whichrotation is eventually transferred through a gearing system or the liketo drive the axle shaft 24. A motive force from, for example, an enginemay be supplied directly to the input shaft 12 or indirectly by means ofa pulley 26. For a more detailed description of the principles ofoperation of such a hydrostatic transaxle, the reader is referred toU.S. Pat. Nos. 5,201,692 and 6,122,996 which are incorporated herein byreference in their entirety.

To house these components, each HZT 10 is provided with a casing whereinthe casings of each HZT 10L and 10R are generally mirror images of oneanother. In one embodiment, the casing is comprised of first casingmembers 28L and 28R and second casing members 30L and 30R (in the formof end caps) that are joined along a substantially vertical junctionsurface 32, as is illustrated in FIGS. 1–4. In this embodiment, foraccepting fasteners 52, each of the HZTs 10 can be provided with aplurality of bosses 54 (illustrated as three by way of example only)having fastener accepting openings. The fasteners 52 are passed throughthe fastener accepting openings of adjacent bosses 54 (which may beformed in both the first and second casing sections or one of the casingsections alone) to mate the HZTs 10L and 10R to form the integratedunit. The casing of each HZT 10L and 10R can also be provided with aflat surface 56 that engages the flat surface 56 of the opposite HZT 10to provide an additional point of contact between the HZTs 10. Thus, theindividual HZTs 10L and 10R also may be joined along a substantiallyvertical junction surface to thereby form the integrated, zero-turn,hydrostatic transaxle assembly.

To maintain the attachment between the HZTs 10L and 10R, a bracket 58may be fastened between each of the HZT casings as illustrated in FIGS.1–3. For this same purpose and by way of further example, a rod 59having opposing threads that are adapted to engage correspondinglythreaded apertures formed in the casings of the HZTs 10 may be utilized.Still further, a threaded rod may pass through un-threaded openings inthe casings and nuts may be threaded to the rod to maintain theattachment between the HZTs 10. In yet another configuration, one ormore bosses on the front portions of the casings of the HZTs 10 may befastened to a vehicle frame to resist torque induced by movement of theaxle shafts 24 and maintain the orientation of the HZTs 10L and 10R withrespect to one another. This fastening technique may be used alone or inconjunction with other fastening techniques such as the aforementionedbracket 58 or threaded rod 59.

As illustrated in FIGS. 6 and 8, the casing may alternatively bearranged such that the second casing sections 30 are replaced by asingle, unitary casing section 31 to which each of the first casingsections 28 are attached. In this case, the casing section 31 generallycomprises a plate having openings for accepting the fasteners and thejunction or sealing surfaces 32 between the casing section 31 and thefirst casing sections 28 lie in parallel, vertical planes. In thisembodiment, there is minimal fluid transfer between the two unitsbecause of the high tolerances involved in the fit of various shaftsinto the bores. It will be appreciated that the illustrated bores neednot be through holes but could be partially bored to accept the shaftsof each unit while leaving an intermediate sealing surface. Bearings maybe inserted into the bores, but these may or may not be necessarydepending upon anticipated loads. The casing section 31 (as well as theplate member 33 described below) may be fabricated from bar stock, bedie cast, or the like.

Still further, as illustrated in FIGS. 7 and 9, the casing may comprisea plate member 33 adapted to be attached over the interface of one orboth of the first casing sections 28 at a vertical junction surface. Inthis embodiment, the first casing sections 28 of both HZTs 10 would beattached directly to one another at a single sealing surface usingfasteners that pass through the openings in adjacent bosses. As a resultof the joining of the first casing sections 28, the plate member(s) 33would be located internally with respect to the attached casing sections28. The plate member(s) 33 could be used to prevent movement of fluidfrom one HZT 10 to the other HZT 10 or allow for minimal leakage acrossbearings, cross holes, portings, and/or the like to allow for a singlefluid fill. In the embodiment particularly illustrated in FIG. 8, crossholes are provided to accept the various shafts of the HZT 10.

In each of the illustrated embodiments, vertically extending from thetop of the first casing member 28 is the input shaft 12 and horizontallyextending from and supported by the first casing member 28 is the axleshaft 24. Thus, the axis of the axle shaft 24 is generally perpendicularto the substantially vertical junction surfaces of the casing.Similarly, the plane of the pump running surface 34 of the centersection 20 is generally perpendicular to the substantially verticaljunction surfaces while the plane of the motor running surface 36 of thecenter section 20 is generally parallel to the substantially verticaljunction surfaces. The axis of the motor shaft 22 is also seen to begenerally parallel to the axis of the axle shaft 24. It is to beunderstood, however, that this arrangement of components is merelyillustrative and that the components can be otherwise arranged withoutdeparting from the scope of this invention.

For placing the hydraulic pump 14 in fluid communication with thehydraulic motor 18, the center section 20 includes hydraulic porting P,as is illustrated in FIGS. 25–28. As will be further seen in thesefigures as well as FIG. 24, the center sections 20L and 20R of each ofthe HZTs 10L and 10R, respectively, are generally mirror images of oneanother. However, since the input shafts 24 are rotated in the samedirection when the vehicle is driven in the forward or reversedirection, the intersection of the kidneys, formed on the runningsurface 34, and the cross passages of the porting P are symmetrical asseen in FIG. 26. It will be appreciated, however, that the centersections 20L and 20R can be full mirror images of one another in thecase where the angular rotation of the swash plates of each HZT are madenon-symmetrical, i.e., the angle of rotation of the swash plates arereversed with respect to one another.

The hydraulic porting P is in further fluid communication with a sourceof makeup fluid, such as a fluid sump or a charge gallery, for example,by means of check plugs 60. Generally, the hydraulic porting P comprisesa high pressure side through which fluid moves from the hydraulic pump14 to the hydraulic motor 18 and a low pressure side through which fluidreturns from the hydraulic motor 18 to the hydraulic pump 14. Since thecenter sections 20L and 20R are generally mirror images of one another,it will be appreciated that similar hydraulic porting P will be utilizedwhen both the HZTs 10L and I0R are placed in the forward or reversedirection. This arrangement of the center section porting P provideseach of the HZTs 10L and 10R with nearly identical hydraulicefficiencies.

To minimize the introduction of impurities, such as metal shavings, intothe hydraulic circuit when makeup fluid is drawn into the hydrauliccircuit, an upward facing filter assembly 62, illustrated in FIG. 28,may be positioned adjacent to the center section 20 through which fluidmay pass from the sump to the hydraulic porting P. The upward facingfilter assembly 62 reduces the potential that air is ingested into thehydraulic porting P as it provides an upward facing exit path for theair. This is especially the case when the filter assembly 62 ispositioned in a generally non-turbulent area of operation within the HZT10.

By way of example, the filter assembly 62 may be comprised of an upperfilter member 64 that carries the filtering mesh. The upper filtermember 64 is positioned adjacent to the center section 20. Attached tothe upper filter member 64, for example by being snap-fit thereto, is alower filter member 66 that forms a seal with the upper filter member 64such that make-up enter the interior formed by the joined upper andlower filter members 64 and 66 substantially via the filtering mesh. Theattached upper filter member 64 and lower filter member 66 may bemaintained in position relative to the center section 20 by means of thecheck plugs 60 the ends of which extend into the interior formed by thejoined upper and lower filter member 64 and 66. Carried by the lowerfilter member 66 may be a magnet 68 and a deflector shield 70 forprotecting the lower filter member 66 from fluid expelled via the checkplugs 60. The magnet 68 is preferably molded into the lower filtermember 66 although it may be attached to the lower filter member 66using an adhesive, for example, as shown in FIG. 1 of U.S. Pat. No.5,613,409 which is incorporated herein by reference in its entirety orby snap-fit engagement, a staking process, or the like. The deflectorshield 70 is attached to the lower filter member 66 by tabs 69 that areformed during the molding process. The deflector shield 70 may also beretained by heat staking to plastic posts, fasteners, or the like.

For attaching the center section 20 to the first casing member 28,fasteners 40 (e.g., bolts) may be passed through openings 42 formed inthe center section 20 to mate with attachment points 44 (e.g., threadedholes) formed in the first casing member 28. In an embodimentillustrated in FIGS. 4, 16, 17 and 24–28, the center section 20 isformed with three extensions 46 each having an opening 42. A first oneof the extensions 46 a extends from a side of the center section 20proximate to the motor running surface 36, a second one of theextensions 46 b extends from a side of the center section 20 proximateto the pump running surface 34, and a third one of the extensions 46 cextends from the bottom of the center section 20. The axis of theopenings 42 are parallel to the axis of the opening 72 through which themotor shaft 22 passes.

For use in orienting the center section 20 within the first housingsection 28, a side of the center section 20 may be provided with aprotuberance 48, e.g., a machined diameter, that extends from the centersection 20 proximate to the pump running surface 34. The protuberance 48is adapted to mate with a center section locator 50 formed in the firstcasing member 28 and to thereby establish an arbitrary X-Y orientationof the central axis of the protuberance 48 and one locating point of thecenter section 20. The axis of the protuberance 48 is also parallel tothe axis of the openings 42 and to the axis of the opening 72 throughwhich the motor shaft 22 passes. Meanwhile, on extension 46 a are a pairof flats 47, located on the top and bottom of extension 46 a asillustrated in FIG. 28, that are adapted to mate with features 49 formedin the first casing member 28 to locate the center section 20rotationally, as illustrated in FIG. 16. The mating of the fasteners 40to the first casing member 28 then provides a Z-axis locator for thecenter section 20 as illustrated in FIGS. 18 and 19.

For adjusting the amount of oil that is pushed from the hydraulic pump14 to the hydraulic motor 18 via the high pressure side of the hydraulicporting P, each HZT 10 includes a moveable swash plate 74 against whichthe pump pistons 16 travel. The direction of rotation of the hydraulicpump 14 is fixed by the rotation of the input shaft 12. The hydraulicpump 14 is nearly always rotated in one direction. As will be understoodby those of ordinary skill in the art, the swash plate 74 may be movedto a variety of positions to vary the stroke of the pump pistons 16 andthe direction of rotation of the hydraulic motor 18. Generally, as theswash plate 74 angle is varied in one direction from the neutralposition the stroke of the pump pistons 16 is varied, which then drivesthe hydraulic motor 18 in a direction determined by the hydraulicporting at a speed determined by the volume of the fluid displaced bythe pump pistons 16 and the torque delivered by the input shaft 12. Aswill be appreciated, rotation of the hydraulic motor 18 results from themotor pistons 19 moving against a thrust bearing 76 under the influenceof the hydraulic fluid. As the angle of the swash plate 74 is decreasedto pass through the neutral position, the direction of rotation of thehydraulic motor 18 is reversed and the speed of the hydraulic motor 18is again determined by the volume of fluid displaced by the pump pistons16 and the torque delivered by the input shaft 12.

Since the speed of rotation of the hydraulic motor 18 is dependent uponthe amount of hydraulic fluid pumped thereinto by the hydraulic pump 16and the direction of rotation of the hydraulic motor 18 is dependentupon the direction of angular rotation of the swash plate 74, thepositioning of the swash plate 74 is seen to control the speed anddirection of rotation of the hydraulic motor 18 and, as will beapparent, the speed and direction of rotation of the axle shaft 24.While it is true that the direction of rotation of the hydraulic motor18 will be affected by the rotation of the hydraulic pump 16, thevariation of rotation from one direction to another is accomplishedcompletely by the swash plate 74.

For moving the swash plate 74, the swash plate 74 is supported by a pairof trunnion arms 78 that are rotatably supported in the casing of theHZT 10 as illustrated in FIGS. 18 and 19. As will be appreciated,rotation of the trunnion arms 78 changes the angular orientation of theswash plate 74 with respect to the pump pistons 16. To rotate thetrunnion arms 78 and, accordingly, move the swash plate 74, a speedadjusting mechanism is coupled to one of the trunnion arms 78. A controlarm 80 of the speed adjusting mechanism may be connected, via a drivinglink, to a lever or a pedal provided on a vehicle whereby movement ofthe lever or pedal is translated to the control arm 80 to cause therotation of the trunnion arms 78 and movement of the swash plateassembly. A further, exemplary speed adjusting mechanism with a returnto neutral mechanism 41 is illustrated in FIG. 8 of U.S. patentapplication Ser. No. 09/789,419 and which is incorporated herein byreference in its entirety.

It is to be further appreciated that the control arm 80 may be locatedon either the outboard or inboard side of the casing of HZT 10, asillustrated in FIGS. 18 and 19, respectively. To this end, the firstcasing member 28 may be provided with a pair of opposed bearing seats 82in which the trunnion arms 78 are carried. The casing may then haveopenings adjacent to both of the bearing seats 82, illustrated in FIG.19, by which the control arm 80 can be attached to one of the trunnionarms 78. Thus, depending upon the desired location for the control arm80, the control arm 80 would be mated to one of the trunnion arms 78 byway of one of the openings and the opposite opening would be closed witha seal 84. Alternatively, the casing can have an opening adjacent tojust one of the bearing seats 82, as illustrated in FIG. 18. In thiscase, it will be appreciated that the location of the single openingwill dictate whether the control arm 80 is mounted on the inboard sideor the outboard side of the casing of the HZT 10. It will be furtherappreciated that when it is desired to have an inboard control arm 80 onan integrated, zero-turn, hydrostatic transaxle assembly, sufficientspacing is to be provided between the joined casings of the HZTs 10L and10R, similar to but larger than the spacing illustrated in FIGS. 1 and2. The spacing is used to accommodate the control arms 80 (as well asany inboard braking mechanisms that are described hereinafter).

For limiting the range of motion of the control arm 80, the control arm80 may be provided with a slot 86 that cooperates with a stop 88, suchas a bolt or the like, attached to the casing as illustrated in FIG. 14.It will also be appreciated that the control arm 80 may be locked intothe neutral position, for example during shipment of the HZT 10 and/orduring assembly into a vehicle. To this end, as illustrated in FIG. 1, anut 90 may be attached to the stop 88 to frictionally engage the controlarm mechanism and thereby prevent its movement. The slot 86 of thecontrol arm 80 may be asymmetrical to thereby allow a greater speed tobe imparted to the axle 24 in the forward direction as compared to thereverse direction.

To provide a space for hydraulic fluid to expand into during operationof the HZT 10, each HZT 10 may include an internally located expansiontank 92 as illustrated in FIGS. 16 and 17. In the illustratedembodiment, the expansion tank 92 is positioned within the HZT casingadjacent to a bull gear 94 that is used to drive the axle shaft 24.Venting of the expansion tank 92 to atmosphere is accomplished via abreather tube 96 that extends from a top of the casing of the HZT 10.Such an expansion tank may be seen in U.S. patent application Ser. No.10/062,734, that is incorporated herein by reference in its entirety.Fluid may be added to the HZT 10 by means of an oil fill port 98 that isalso formed on the top of the casing of the HZT 10. Further, theexpansion tank cover 91 may be provided with an indentation 93 and athumb stop 95 (that extends below the sealing surface) by which theexpansion tank cover 91 may be grasped for insertion into the firstcasing section 28. The indentation 93 is particularly sized to accept afinger of the installer. In this manner, the expansion tank cover 91 maybe installed while allowing the user to avoid contacting sealant carriedon the sealing surface of the cover 91.

To enable the vehicle on which the HZTs 10 are mounted to roll or“freewheel” without resistance from the hydraulic fluid, each HZT 10 mayinclude a hydraulic bypass. Generally, when an HZT 10 does not have amotive force being applied to it, the hydraulic pump 14 and thehydraulic motor 18 are not being rotated. Therefore, any attempt to rollthe vehicle would transmit rotational energy through axle shaft 24 tothe motor shaft 22, via any internal gearing, thereby causing thehydraulic motor 18 to rotate. The rotation of the hydraulic motor 18,and the action of motor pistons 19 against motor thrust bearing 76,causes fluid to flow through the hydraulic porting P of the centersection 20 to the hydraulic pump 14. However, with the hydraulic pump 14being in neutral, the resultant pressure causes resistance to motion ofthe motor shaft 22 and the axle shaft 24 and prevents the user fromeasily pushing the vehicle.

To solve this problem, a bypass mechanism 100 may be associated with thehydraulic circuit to allow fluid to flow between the high pressure sideand the low pressure side of the center section 20 porting. The bypassmechanism 100, illustrated in FIG. 23, may be activated via rotation ofa bypass arm 102 that is located proximate to the top of the casing ofthe HZT 10. The bypass arm 102 is linked to a bypass actuator 104 that,in turn, interfaces with the center section 20 at its distal end. Thedegree of movement of the bypass arm 102 may be controlled by providingthe control arm 102 with a notch 103 the shoulders of which are adaptedto engage a stop 105 formed on the casing to limit how far the bypassarm 102 may be rotated.

In order to locate the relatively featureless bypass actuator 104 withinthe casing, a retaining ring 110 is attached to a groove in the bypassactuator 104. Once the bypass actuator 104 and retaining ring 110 areinstalled, a second retaining ring 106 is installed to keep retainingring 110 in place. A seal 112 may also be placed adjacent to theretaining ring 110.

The bypass arm 102 interfaces with bypass actuator 104 by means of atapered flat surface that prevents relative rotation between the bypassactuator 104 and the bypass arm 102. Push nut 108 aids in maintainingengagement between the bypass arm 102 and the bypass actuator 104. Inthis manner, rotation of the bypass actuator 104, via the bypass arm102, can be used to move a puck, pin, or the like to lift the hydraulicmotor 18 off of the motor running surface of the center section 20 tobreak the hydraulic circuit and thereby allow for freewheeling asdescribed in U.S. Pat. Nos. 5,201,692, 5,423,182, and 5,497,623 whichare incorporated herein by reference in their entirety.

To drive the axle shaft 24, gearing may be provided that functions todrivingly couple the axle shaft 24 to the motor shaft 22. By way ofexample, with reference to FIGS. 16 and 17, the motor shaft 22 mayinclude a drive gear 114 that drivingly engages one or more reductiongears 116 that drive the bull gear 94 which, in turn, drivingly engagesthe axle shaft 24. In the illustrative embodiment, two reduction gears116 a and 116 b are provided wherein the first reduction gear 116 aengages the drive gear 114 and drives the second reduction gear 116 bthat is set within the inside diameter of the first reduction gear 116a. The second reduction gear 116 b drives the bull gear 94.

As further illustrated in FIG. 22, a proximal end of the axle shaft 24is carried by an inboard bushing 118 positioned within the first casingsection 28 adjacent to the bull gear 94. Axial movement of the axleshaft 24 in an inward direction towards the bull gear 94 is preventedsince the proximal end of the axle shaft 24 is restrained by contactingan interior wall of the first casing section 28. Axial movement of theaxle shaft 24 in an outward direction may be prevented through the useof a retaining ring positioned adjacent to the inward side of the bullgear 94. The first casing section 28 also includes an axle horn in whichis carried an outboard bushing 120 that provides additional support forthe axle shaft 24. A seal and retaining ring pack 122 is positioned inthe axle horn on the outboard side of the bushing 120. It is to beunderstood that the distal end of the axle shaft 24 is adapted to have avehicle wheel mounted thereto.

For allowing a brake mechanism 123 to be mounted to either the inboardor outboard side of the casing of the HZT 10, the motor shaft 22 canextend from the inboard side or the outboard side of the first casingsection 28 as seen in FIGS. 20 and 21. It will be appreciated that thebrake mechanism 123 may be a disc brake mechanism, as illustrated inFIG. 10, a cogged parking brake as illustrated in FIG. 11, or the like.As further illustrated in FIGS. 20 and 21, the motor shaft 22 may beprovided with a configuration that depends upon whether the brakemechanism 123 is to be mounted on the inboard or outboard side of thecasing. In this regard, three motor/brake shaft options are available.First, the motor/brake shaft could extend simultaneously from both theinboard and outboard side of the casing of the HZT 10 (not shown).Second, as illustrated in FIG. 21, the second casing section 30 can havean opening to accommodate the motor shaft 22 for inboard mountingthereof and the motor/brake shaft would not extend through the firstcasing section 28. Third, as illustrated in FIG. 20, the second casingsection 30 can be used to cover and support one end of the motor/brakeshaft while the opposite end of the motor/brake shaft extends from thefirst casing section 28 to the outboard side of the HZT 10. It will beappreciated that the first option increases the flexibility of the HZT10 while the second and third options provide for a lower costmotor/brake shaft while eliminating the need for extra machining andseals.

When a brake mechanism is positioned on the inboard side of both theHZTs 10L and 10R, an integrated brake unit can be utilized asillustrated in FIG. 5. By way of example, the integrated brake unit maycomprise a first brake disk 124L mounted to the motor shaft 22 of HZT10L that is cooperable with a second brake disk 124R mounted to themotor shaft 22 of HZT 10R. The brake disks 124 may be provided withsplines that are adapted to mate with corresponding splines formed onthe motor shafts 22. Furthermore, when the HZTs 10L and 10R are mated,the spacing between the motor shafts 22 is not sufficient to allow thebrake disks 124 to separate from their engagement with their respectivemotor shaft 22. It is contemplated that the spacing between the motorshafts 22 may be such that the brake disks 124 are in slippingengagement with one another when the brake mechanism is not activated.

To drive the brake disks 124 into frictional engagement with oneanother, a brake actuator 126, which can be a wire form, stamped metal,powdered metal piece, constructed using a cold heading process, etc.,may be mounted to one of the HZT casings. Generally, the actuator 126comprises an arm that is used to rotate the brake actuator 126 and a camwhich, when the actuator 126 is rotated, is used to drive the brakedisks 124R and 124L into frictional engagement. More specifically, thecam of the actuator arm 126 is used to drive a brake puck 128, via aprotecting brake puck plate 130, into a first one of the brake disks 124to, in turn, drive the first one of the brake disks 124 into the secondone of the disk brakes 124. A second brake puck 132, associated with thesecond one of the disk brakes 124, is used to prevent movement of thesecond one of the disk brakes 124 under the influence of the drivingfirst one of the disk brakes 124 to thereby maintain the frictionalengagement. It will be appreciated that additional brake disks (notillustrated) may be utilized. It is to be further appreciated that theillustrated brake mechanism can also provide for the use of a brakeyoke.

For maintaining the positioning of the brake pucks 128 and 132 withinthe brake mechanism, the casings of the HZTs 10 may include a groovedportion 134 sized and arranged to accept the brake puck. It will beappreciated that the positioning of the corresponding brake disk 124functions to prevent the brake puck from dislodging from the groove 134in which it is positioned. A further groove 136 may be provided in thecasing of the HZT 10 in which the actuator 126 is positioned. Thisgroove 136 may extend into and add to the grooved portions 134 tothereby allow the cam of the actuator 126 to be positioned behind thebrake puck and brake puck plate 130. It is to be understood that thewire form, brake actuator 126 may be used in other configurations suchas with a single or multiple disk brake and a brake yoke in place of amating housing.

For maintaining the brake actuator 126 on the casing of the HZT 10, aretaining bracket 138 may be provided. The retaining bracket 138 may beattached to the casing by means of the fastener 139 used to mate thefirst and second casing sections 28 and 30. A separate fastener 140adapted to mate with the second casing section 30 may also be utilizedfor this same purpose. The brake puck plate 130, the brake puck 128, andthe brake disk 124 also function to keep the actuator 126 retained onthe casing of the HZT 10 given the proximity of these components to oneanother and the mating features formed in the housing and shaft of theactuator 126.

To provide for the easy mounting of the HZT 10 to a vehicle frame, thefirst casing section 28 of each HZT 10 includes a plurality of fasteneraccepting openings 142. As illustrated in FIGS. 12–15, a pair offastener accepting openings 142 can be positioned on opposing sides ofthe first casing section 28 and a further plurality of fasteneraccepting openings 142 can be positioned on the axle shaft horn of thefirst casing section 28. While illustrated with four fastener acceptingopenings 142 being formed on the axle shaft horn of the first casingsection 28, it is to be appreciated that this is not intended to belimiting. Rather, any number of fastener accepting openings 142 can beformed and/or utilized in the attachment process. Still further,fastener accepting openings could be formed on a bracket 58 for use inmounting the HZTs 10L and 10R to a vehicle frame.

For use in cooling the EZTs I0L and 10R, a fan 150 may be mounted to oneor both of the input shafts 12 adjacent to the pulley 26 as isillustrated in FIGS. 1 and 3. When two fans 150 are utilized, thediameters of the fans 150 need to be such that they do not contact eachother while turning. Alternatively, if the fans 150 do have overlappingdiameters, the fans 150 need to be vertically spaced to prevent bladecontact. While specific embodiments of the invention have been describedin detail, it will be appreciated by those skilled in the art thatvarious modifications and alternatives to those details could bedeveloped in light of the overall teachings of the disclosure.Accordingly, the particular arrangement disclosed is meant to beillustrative only and not limiting as to the scope of the inventionwhich is to be given the full breadth of the appended claims and anyequivalents thereof.

1. A center section for a hydrostatic transaxle comprising a casingcarrying a hydraulic pump driven by an input shaft and a hydraulic motordrivingly linked to an axle shaft, the hydraulic pump being in fluidcommunication with the hydraulic motor via porting formed in the centersection to transfer a motive force received via the input shaft to thehydraulic motor to drive the axle shaft, wherein the center sectioncomprises: a pump running surface on which the hydraulic pump isrotationally mounted; a motor running surface on which the hydraulicmotor is rotationally mounted; a protuberance adapted to mate with acenter section locator formed in the casing to establish an X-Yorientation for a central axis of the protuberance; a pair of flatsadapted to mate with features formed in the casing to locate the centersection rotationally; and at least one opening for a fastener thatprovides a Z-axis locator for the center section.
 2. The center sectionof claim 1, wherein the center section comprises a plurality ofextensions, each having one opening for accepting a fastener.
 3. Thecenter section of claim 2, wherein a first one of the plurality ofextensions extends from the center section proximate to the pump runningsurface, a second one of the plurality of extensions extends from thecenter section proximate to the motor running surface, and a third oneof the plurality of extensions extends from a portion of the centersection intermediate the first and second extensions.
 4. The centersection of claim 3, wherein the pair of flats are formed on one of theplurality of extensions.
 5. The center section of claim 4, wherein thepair of flats are formed on a top side and a bottom side of the one ofthe plurality of extensions.
 6. The center section of claim 2, whereinthe axis of the protuberance is parallel to the axis of each of theopenings.
 7. The center section of claim 1, wherein the motor runningsurface includes an opening for accepting a hydraulic motor shaftassociated with the hydraulic motor and the axis of opening in the motorrunning surface is parallel to the axis of the protuberance.
 8. Thecenter section of claim 1, wherein the casing is formed of at least afirst portion and a second portion mated together along a joint surface.9. The center section of claim 8, wherein the protuberance has an axisthat is generally perpendicular to the joint surface.
 10. A centersection for a hydrostatic transaxle comprising a casing carrying ahydraulic pump driven by an input shaft and a hydraulic motor drivinglylinked to an axle shaft, the hydraulic pump being in fluid communicationwith the hydraulic motor via porting formed in the center section totransfer a motive force received via the input shaft to the hydraulicmotor to drive the axle shaft, wherein the center section comprises: apump running surface on which the hydraulic pump is rotationallymounted; a motor running surface of which the hydraulic motor isrotationally mounted; at least one fastener opening; and a cylindricalprotuberance formed on the center section and adapted to mate with acenter section locator formed in the casing.
 11. The center section ofclaim 10, wherein the fastener opening is parallel to the protuberance.12. The center section of claim 10, further comprising a pair of flatsurfaces adapted to mate with the casing.
 13. The center section ofclaim 12, wherein the pair of flat surfaces are disposed about thefastener opening.
 14. The center section of claim 10, further comprisinga plurality of fastener openings wherein at least two of the openingsare generally at opposite ends of the center section.
 15. The centersection of claim 14, comprising an additional fastener opening locatedbetween the two openings at opposite ends of the center section.
 16. Thecenter section of claim 15, wherein the additional fastener opening hasa central axis that is parallel to the plane of the pump running surfaceand wherein the additional fastener opening is near an edge of thecenter section opposite the pump running surface.
 17. The center sectionof claim 10, wherein the protuberance has a diameter less than thediameter of the pump running surface.
 18. The center section of claim10, wherein the protuberance is perpendicular and adjacent to valveopenings formed in the center section.
 19. A center section for ahydrostatic transaxle comprising a casing carrying a hydraulic pumpdriven by an input shaft and a hydraulic motor drivingly linked to anaxle shaft, the hydraulic pump being in fluid communication with thehydraulic motor via porting formed in the center section to transfer amotive force received via the input shaft to the hydraulic motor todrive the axle shaft, wherein the center section comprises a means forlocating the center section in the casing, wherein the means comprises aprotuberance formed on the center section, a pair of flat surfaces onthe center section separate from the protuberance and at least onefastener opening formed in the center section for receiving a fastenerengaged to the casing.
 20. The center section of claim 19, wherein thepair of flat surfaces are on opposite sides of the fastener opening. 21.The center section of claim 19, wherein the protuberance is positionedon one side of the motor running surface and the pair of flats ispositioned on the opposite side of the motor running surface.
 22. Thecenter section of claim 19, further comprising a plurality of fasteneropenings.
 23. The center section of claim 22, wherein the plurality offastener openings includes a fastener opening adjacent the pair of flatsurfaces near an end of the center section and a fastener opening nearthe opposite end of the center section.
 24. The center section of claim19, wherein the center section comprises a motor shaft opening andwherein the axis of the protuberance is parallel to the motor shatopening.